Early protein malnutrition changes learning and memory in spaced but not in condensed trials in the Morris water-maze

Early protein malnutrition induces structural, neurochemical and functional changes in the central nervous system leading to alterations in cognitive and behavioral development of rats. The aim of the present study was to investigate the effects of protein malnutrition during lactation on acquisition and retention of spatial information using different training procedures (spaced x condensed trials). Rats treated with 16% (well-nourished) or 6% (malnourished) protein diets during the lactation phase and nutritionally recovered until 70 days of age were tested in the Morris water-maze in procedures of 1 trial/day (spaced trials), 4, 8, 12 trials/day (intermediate density) and 24 trials/day (condensed trials), completing 24 trials at the end of training. Seven and 28 days after the training the animals were tested again in just one trial to assess long-term memory. The results showed that protein malnutrition caused deficits on the spatial learning and memory in spaced but not in intermediate and condensed trials procedure. Seven and 28 days after the training there was an increase in the latency to find the platform but only malnourished animals submitted to 1 trial/day had significantly higher latency as compared with well-nourished controls. One of the possible hypotheses is that the effect protein malnutrition only in the procedure of spaced trials could be due to deficits in memory consolidation. It is suggested that these deficits can be the result of alterations produced by protein malnutrition in the hippocampal formation or in long-lasting emotional and/or motivational aspects of the rat's behavior.